OIA1008 SURFACTANTS

What is a surfactant?

A substance that adsorbs onto surfaces/interfaces at low concentration and significantly reduces surface or interfacial tension.

What is the main role of surfactants in pharmacy?

To reduce surface/interfacial tension, enabling emulsification, solubilization, dispersion, and improved drug bioavailability.

Why are surfactants called amphiphilic?

They have both hydrophilic (water-loving) heads and hydrophobic (oil-loving) tails.

How do surfactants lower surface tension at the air-water interface?

By disrupting cohesive forces between water molecules.

What are the four types of surfactants based on charge?

Anionic, cationic, nonionic, and zwitterionic (amphoteric).

What is the defining feature of anionic surfactants?

They have a negatively charged hydrophilic group.

When are anionic surfactants most effective?

In removing dirt, clay, and oily stains—used in soaps and shampoos.

Give an example of an anionic surfactant used in personal care.

Sodium lauryl sulfate (SLS), used in toothpastes and shampoos.

What is SDS and where is it used?

Sodium dodecyl sulfate—used in hygiene and cleaning products.

How are anionic surfactants like soaps obtained?

Via saponification of triglycerides (fats) with alkali.

What charge do cationic surfactants carry?

Positive charge on their hydrophilic group.

Where are cationic surfactants commonly used?

In antistatic products like fabric softeners and as disinfectants.

Name a cationic surfactant with antimicrobial activity.

Cetylpyridinium chloride—used in mouthwashes and lozenges.

What makes amphoteric surfactants unique?

They have both positive and negative charges depending on pH.

What are the advantages of amphoteric surfactants?

Low toxicity, antibacterial properties, and compatibility with other surfactants.

Give an example of a zwitterionic surfactant used in cosmetics.

Cocamidopropyl betaine—used in shampoos and body washes.

What distinguishes nonionic surfactants?

They lack charge and are based on hydrophilic EO chains.

Where are nonionic surfactants commonly used?

As emulsifiers and foaming agents in pharmaceuticals.

Name a nonionic surfactant used in drug formulations.

Polysorbate 20 (Tween 20)—used to stabilize emulsions.

What does the HLB value of a surfactant represent?

The balance between its hydrophilic and lipophilic parts.

What does a low HLB value (<10) indicate?

The surfactant is more lipophilic—suitable for W/O emulsions.

What does a high HLB value (>10) indicate?

The surfactant is more hydrophilic—suitable for O/W emulsions.

How does ethoxylation affect HLB?

More EO units = higher HLB = more water solubility.

What is a micelle?

An aggregate of surfactant molecules with hydrophobic cores and hydrophilic shells.

What is the critical micelle concentration (CMC)?

The minimum surfactant concentration required to form micelles.

What drives micelle formation thermodynamically?

Decreased system free energy via hydrophobic fragment removal and hydrogen bond formation.

How can micelle size and shape be controlled?

By adjusting surfactant structure, concentration, pH, and ionic strength.

How does counterion affect micelle size in anionic surfactants?

Larger counterions (e.g., Cs⁺) increase micelle size: Na⁺ < K⁺ < Cs⁺.

What is micellar solubilization?

Increasing solubility of poorly water-soluble drugs via entrapment in micelles.

What role does CMC play in solubilization?

Solubilization begins at or above the CMC.

What happens when micelle concentration increases?

Drug solubility increases proportionally.

Name surfactants approved by the FDA for parenteral solubilization.

Polysorbate 20, 40, 80; monopalmitate; polyoxyethylated fatty acids.

How do surfactants aid emulsification?

By reducing interfacial tension between oil and water phases.

How do surfactants assist in drug delivery systems?

By improving drug solubility, stability, and absorption.

Why are surfactants included in topical formulations?

For spreading, wetting, and enhanced skin penetration.

How do surfactants function in oral care products?

As antimicrobial and foaming agents (e.g., cetylpyridinium chloride in mouthwash).

What is the critical micellization temperature (CMT)?

The temperature above which micelles start forming.

How can micelles change structure?

Spherical → cylindrical → bilayers, depending on surfactant properties.

How does ionic strength influence micellization?

Higher ionic strength often promotes larger micelles due to charge shielding.

What is the pharmaceutical relevance of micelle formation?

Allows formulation of injectable and oral drugs that are otherwise water-insoluble.